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Tension Elements.

579

Advantages.

6. BELT GEARING.

Disadvantages.

Useful in connection with shafting
as a distributor and modifier with
comparatively few parts.

Easily started and stopped.

Practically noiseless.

Very convenient for bridging rea-
sonable distances.

Large pull on bearings, but in well-
lubricated bearings friction does not
depend on pressure.

Slip an advantage in case of shock.

Frictional loss principally in the
line shafting: about 257,, to 50% in
a shop system.

Large belts with heavy pressures
are expensive to maintain.

Slip   a  disadvantage   where  exact
velocity ratio is required.

7. COTTON-ROPE GEARING.

For fairly long-distance driving in
mills, and for travelling cranes.

Better grip than belts, due to wedge-
groove pulleys.

Quite noiseless.

Separate driving to the various
floors of a mill occasions less loss of
time in breakdowns.

Small liability to break down also.

Frictional and other losses probably
somewhat larger than with belt gear-
ing, due to heavy pullies and fly-
wheels.

Working speeds being high, rope
tension is increased 5o/0 by centri-
fugal force : but bearing pressures are
not thereby affected.

8. WIRE-ROPE GEARING.

Suitable for very long distances, say
for several miles, when relays are
adopted. Cases quoted in text.

If moderate speeds be employed,
little increased tension from centri-
fugal force.

Frictional and other losses 22S/0
per mile, not including motor and
machines: lesser and greater distances
in proportion.

9. PITCH-CHAIN GEARING.

As useful as belt driving in de-
creasing the number of parts while
modifying the power: but gives at
the same time positive transmission,
and may be used with heavy loads.

Adapted for high as well as low
speeds if well made, but the former
should go with light pressures.

Frictional loss depends very much
on design and manufacture, and pro-
bably varies from 5% to 3O/0 in a
pair of wheels: there being two sets
of friction surfaces, not including the
journals.

Increase of pitch after wear causes
excessive friction and bad working.